Using data from the Fragile Families and Child Wellbeing Study (N = 2,656), we examined the association between intergenerational relationships and parents' union stability 5 years after a baby's birth. Results showed that more amiable relationships between parents and each partner's parents, and children's spending more time with paternal grandparents, increased the odds that parents coresided by the time their child was age 5. The more time that children spent with maternal grandparents reduced union stability, although this result was not robust to methods that better address selection. These findings underscore the importance of the broader social contexts affecting couple stability and suggest that even amid demographic changes, intergenerational family ties are important for couples and, by extension, their children.